Introduction
Weather is dynamic – the conditions we see in front of us can change dramatically throughout the course of one day. It is important to gather all the available data, but you will also need to be paying attention to visual information such as clouds, windsocks etc. These indicators may contradict data from the weather reports. On-site, visual data, almost always takes precedence over the weather data you’ve collected. There are a few circumstances where it doesn’t take precedence and will be covered in a later section.
There are two types of weather that you should be familiar with: frontal weather and local weather. Frontal weather occurs when two air masses like cold dry air from Canada, and warm, moist air from the Gulf of Mexico collide and cause a large scale storm that moves across the United States. This is what most weather reports focus on. What are the major weather systems in your area and what sort of weather will they produce? Are you under a low pressure system or a high pressure system? Where is the Jet Stream? Local weather relates to conditions like temperature, humidity, winds aloft, surface winds and topography. Puffy cumulus clouds over mountains are caused by local weather.
There are many types of clouds. Some can indicate good flying, while others can be dangerous or indicate dangerous conditions. Being able to read clouds properly will help you find areas of good lift, and safe conditions. Cloud formations may change rapidly during the day, so you should be constantly analyzing them for signs that the conditions are becoming too extreme, or deteriorating. The next few paragraphs will discuss frontal and local weather, their related clouds, and what they may mean for your flying.
Local Weather
Local weather consists of variables such as ground heating (temperature), humidity, dew-point, anabatic or catabatic flow, winds aloft, surface winds and their interaction with the topography.
As mentioned earlier in this program, local sites have weather patterns that are unique and can change quickly. Listening to your instructors and the local weather gurus can help avoid flying in potentially dangerous situations.
Similar to larger scale frontal weather, clouds can be an indicator of the current conditions. However, not all days will have the conditions required to produce clouds. On days where no clouds are present you will need make an educated guess based solely on the forecasts.
Frontal Weather
Fronts move across the United States from west to east, and clouds in the atmosphere often give us clues that indicate a front is heading our way. If you pay attention to them you can make an educated guess as to how the weather will progress during the day or even over the next few days. Fronts may produce an improvement in the weather or a storm system. Cold fronts tend to move into and across the US from the cold northwest and warm fronts tend to move northeast from the warm Gulf of Mexico. Interesting and active weather usually results when a drier cold front meets a humid warm front.
Surface Wind
Surface wind is our biggest concern when checking weather and the single largest determining factor for flying. If it is too windy to launch and land safely during the times you plan to be flying, your weather data collection can end here and you may break out the fishing gear. As an entry level pilot anything over 12 Mph is generally too strong.
You may obtain surface wind data from flight service, from a nearby airport, or from the internet. Airports often have an automated announcer that will give the current surface winds and the trend over the last few hours. On the internet, wunderground.com or usairnet.com will give you detailed current and forecasted surface wind conditions for your area. Be sure to obtain current and forecasted conditions, so you know what to expect throughout the day. Some days you may be able to fly in the morning knowing that the wind is expected to increase later in the day or vice/versa.
Winds Aloft
The winds aloft are calculated from measurements taken at winds aloft reporting stations located throughout each state. For each reported altitude you want to get wind direction, speed and temperature. The reported altitudes are 3,000 ft, 6,000 ft, 9,000 ft, 12,000 ft, 18,000 ft. Our FAA imposed ceiling is 18,000 feet, so there is little need to collect data above that level. If you are talking to a flight briefer, you will need to know which altitudes and the time frame you want the information for. If you obtain the data off the internet, you will need to understand the format in which it is presented. If the winds aloft within a few thousand feet of the ground are high, the surface winds may increase at some point during the day. You should be absolutely certain they will not increase to unsafe levels quickly and unexpectedly. Like the surface winds, if the winds aloft look too strong during the times you want to fly, there is no need to look further into the weather for that day.
You can fly in higher winds aloft than surface winds, so long as there are no obstacles such as large mountains, or the winds aren’t so strong they threaten to push you into undesirable territory. Generally winds near or above your trim speed are to be avoided. Depending on the thermal strength for the day, winds aloft may “shred” the soft outer edges of the thermals, leaving sharp-edged and unpleasant thermal cores.
When flying in the mountains, keep in mind the altitude and direction of the winds so as not to launch or fly into turbulence (rotor) on the lee side. If you don’t know what the winds aloft are doing, the winds you see at launch may be misleading. This is one of those circumstances where collected weather data and visual observation can contradict and fool you into launching in dangerous conditions.
Some sites, under the right conditions, will do what is called “thermal blocking” where there is enough heat and thermal activity coming off the ground to block out a wind that is blowing from the wrong direction. These can be great conditions, but you should be aware of the prevailing winds aloft, and that the conditions may change quickly. At some point during the day, there will no longer be enough heating, or the winds aloft overpower the heat. Conditions can change very quickly, and you should be prepared to handle them or be out of the air before they change.
When collecting winds aloft data be sure to collect the temperatures at the reported altitudes. This will help you later when figuring out what the thermal potential for the day will be.